1. Field of the Invention
The present invention relates to a method of preparing nanosized spherical vanadium oxide particles and, more particularly, to a method of preparing nanosized spherical vanadium oxide particles having an average particle size of tens of nanometers using a sol-gel method.
2. Description of the Related Art
Divanadium pentaoxide (V2O5) particles are generally prepared using a solid phase method, a liquid phase method, or a vapor phase method. In the solid phase method, divanadium pentaoxide particles are derived from thermal decomposition of ammonium vanadate at a temperature of 400-600xc2x0 C. This solid phase method is relatively easy to perform, but the resulting divanadium pentaoxide particles have irregular shapes and large particle size on the order of several micrometers.
When divanadium pentaoxide particles are prepared using the liquid phase method, there is an advantage of easy processing with efficient control of particle size, crystal phase, and specific surface area. However, the resulting divanadium pentaoxide particles are limited to planar or ribbon shapes, and thus spherical particles cannot be obtained using the liquid phase method.
The vapor phase method is divided according to the type of energy source, i.e., whether laser or plasma is used as an energy source. In preparing divanadium pentaoxide particles, the vapor phase method is difficult to control and is less economical than the liquid phase and solid phase methods.
Recently, there has been an increased interest in using nanosized particles in the development of new functional materials to improve the properties of existing active materials as well as to obtain new properties.
As electronic components have become smaller with increased performance requirements, the size of raw material particles for electronic components has also decreased to the order of submicrons or less. For a uniform and fine distribution of sintering additive particles in a green body, there is a need to reduce the size of the sintering additive particles to a fine level. Reportedly, performance of a sensor is improved by reducing the size of source particles with the effect of increasing active surface area.
Divanadium pentaoxide particles have great electrochemical activity. Thus, divanadium pentaoxide particles are used as catalysts, electrochromic devices, anti-static coating materials, and active materials for sensors and secondary cells. Discharge capacity of a secondary cell can be improved by using a nanosized, ribbon-shaped active material, compared to a secondary cell manufactured using a microsized active material. In additon to the application as active materials for secondary cells, nanosized divanadium pentaoxide particles are expected to show improved performance in applications of catalysts, electrochromic devices, anti-static coating materials, and active materials for sensors. In the above and other applications, spherical particles are needed for better mixing, dispersion, or forming processes. Accordingly, for commercial applications of nanosized divanadium pentaoxide particles, there exists a need for an economic and efficient method for preparing nanosized divanadium pentaoxide particles.
Up to now, however, an economic and efficient method of preparing nanosized divanadium pentaoxide particles having a spherical shape has not been developed.
According to a primary feature of the present invention, a method of preparing nanosized spherical divanadium pentaoxide particles comprises, preparing a vanadium ion-containing aqueous solution by dissolving a vanadium ion-containing material; adding at least one solvent selected from a non-protonic, polar organic solvent and a glycol solvent to the vanadium ion-containing aqueous solution and mixing the same; and aging the mixture.
In preparing the vanadium ion-containing aqueous solution, the vanadium ion-containing material is dissolved in a hydrogen peroxide aqueous solution or an acid aqueous solution. Although the type of the acid aqueous solution that may be used is not limited, a hydrochloric acid aqueous solution, a nitric acid aqueous solution, or a sulfuric acid aqueous solution is preferred.
Preferably, the amount of hydrogen peroxide in the hydrogen peroxide aqueous solution or the amount of acid in the acid aqueous solution is in the range of about 0.5 to 5 times the amount of vanadium ion-containing material in order to fully dissolve the vanadium ion-containing material. If the amount of hydrogen peroxide or the amount of acid exceeds the above stated range, it becomes uneconomical due to a relative low concentration of vanadium ions. If the amount of hydrogen peroxide or the amount of acid is less than the above stated range, it becomes difficult to fully dissolve the vanadium ion-containing material.
Preferably, the vanadium ion-containing aqueous solution contains between about 0.01 to 0.5 M vanadium ion.
In accordance with a preferred embodiment of the present invention, the non-protonic, polar organic solvent is at least one selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylacetamide, hexamethylphosphoamide, and pyridine, and the glycol solvent comprises at least one selected from the group consisting of ethyleneglycol, propyleneglycol, and butyleneglycol. The amount of the solvent is in a preferred range of about 60-98% by volume based on the total volume of the vanadium ion-containing aqueous solution and the solvent.
Aging of the mixture is performed preferably for about 0.5 to 100 hours at a temperature not less than 0xc2x0 C. and not greater than the higher of the boiling point of the vanadium ion-containing aqueous solution and the boiling point of the solvent.
In the method for preparing vanadium oxide particles according to the present invention, any vanadium ion-containing material can be used without limitations, but divanadium pentaoxide is preferred.
These and other features and aspects of the present invention will be readily apparent to those of ordinary skill in the art upon review of the detailed description that follows.